The present disclosure relates generally to methods and apparatus for retaining components in a downhole motor in the event of a mechanical separation or failure of one or more components therein; and more specifically relates to a catch mechanism which may be secured to a desired component in the downhole motor (such as, for example, the rotor of the motor, or a component of a driveshaft assembly, as will typically be coupled to a downhole end of the rotor). As discussed in more detail later herein, the described catch mechanism engages the downhole motor component without requiring a threaded engagement to the component, which is particularly advantageous. The catch mechanism described herein is configured to actuate to dynamically engage a surface of the motor component to secure the catch mechanism in a fixed longitudinal position relative to the component when excessive motion of the motor component occurs.
The use of downhole motors in drilling operations is well known. The most common such downhole motors are positive displacement-type motors, which include a power section having a lobed stator and a differently lobed rotor therein, where pumping of drilling mud through the power section causes rotation of the rotor. The power section is coupled to a transmission assembly, in which a drivetrain assembly is coupled to the rotor and extends through a bearing pack that facilitates changing the eccentric rotation of the rotor to single axis rotation proximate the lower end of the drivetrain assembly.
One concern that can exist with downhole motors is the risk that in the event of a mechanical separation or failure during use in a well, some portion of the rotor, or of the drivetrain assembly coupled thereto, may separate from the remainder of the motor assembly and be lost in the well. In that situation, the drill string will have to be removed from the well, and fishing and/or milling operations performed to remove the separated components from the wellbore. Such remedial efforts are obviously time-consuming and expensive.
In many circumstances, such as where wells are drilled offshore, sometimes to great depths, the drilling can be difficult, with exceptional loads and stress placed upon all components in the drill string, particularly on the driven components of the downhole motor and the other components coupled thereto. As a result, catch mechanisms have been proposed for use with downhole motor components, which threadably couple to the motor component to create an expanded dimension of the catch mechanism sufficient to engage an integral portion of the motor assembly, such as a shoulder extending inwardly from the housing, or another component supported by the housing. Such mechanisms, while generally satisfactory for the catch function, present other difficulties.
After use of a downhole motor, the motor will be torn down and inspected, and in most cases refurbished for another use. Threaded components in the motor drivetrain necessitate a more rigorous examination during such inspections, such as a black light inspection (often by a third party), before refurbishment can occur. Additionally, a threaded component of a downhole motor drivetrain provides a potential disadvantage because of the stresses that can occur in a threaded coupling, as it can represent another potential point of failure. Thus, it would be highly beneficial to have a catch mechanism that engages the downhole motor drivetrain components sufficiently securely to retain the components in the event of a mechanical failure, but without the need for a threaded engagement with a drivetrain component.